1. Field of the Invention
This invention relates to heat exchangers for nuclear reactor systems and, more particularly, to sodium-to-water heat exchangers for liquid metal fast breeder reactors, and the like.
2. Description of the Prior Art
Many industrial processes require apparatus that enables heat to be transferred from one fluid to another. Frequently, these heat exchangers must permit this transfer to take place between fluids that are quite incompatible in one or more ways.
Typically, in a liquid metal fast breeder nuclear power reactor, it is necessary to transfer heat from molten sodium to water in order to generate steam for subsequent use in driving the turbines and associated generators that produce electricity. If the sodium and the water are permitted to mix together, even in relatively minute quantities, there will be a violent chemical reaction which will generate heat, gas and corrosive matter in the vicinity of the leak. An occurrence of this nature, if it is not observed and checked at an early stage, can cause a great deal of damage to the entire heat exchanger structure, or at the very least, it can compel the entire plant to remain idle while an otherwise minor leak is being repaired-an expensive and inefficient state of affairs.
A number of proposals have been advanced to overcome this problem. Illustratively, several heat exchangers, all connected in a manner that enables the water flow to any one of the heat exchangers to be stopped without interferring with the flow of water to any of the other heat exchangers in the event of a leak in any unit has been suggested. The large numbers of small units required in these circumstances, however, impose a significant increase in the cost of the steam generators and other associated power plant systems components.
Several types of double-wall tubes also have been devised, for example, in which an intermediate fluid that does not react violently with either water or sodium fills the volume between the tube walls. This approach to solving the sodium to water heat exchanger leak problem is very expensive, the initial cost of a double wall tube heat exchanger being several times that of a comparable single wall tube heat exchanger.
Accordingly, there is a pressing industrial need to devise a reliable and relatively low-cost heat exchanger that permits heat to be transferred safely between incompatible fluids in spite of a minor leak in the heat exchanger structure.